Hall effect and Current Measurement

Discovered in 1879 by
Edwin H. Hall (1855 – 1938), the Hall field results from the force
exerted by the magnetic field on the moving particles of the current.
The Hall effect can be used to measure certain properties of current
carriers as well as to detect the presence of a current on a magnetic
field.

In "A", the Hall element takes on a negative charge at the top
edge (blue color) and positive at the lower
edge (red color). In "B" and "C", either the electric current or
the magnetic field is reversed, causing the polarization to
reverse. Reversing both current and magnetic field ("D") causes
the Hall element to again assume a negative charge at the upper
edge.